iCloud on Windows 15.0.214 stuck in a sync-loop

I've installed the new iCloud for Windows App to sync photos/videos.

It starts syncing but gets stuck at the same point every time "Syncing 8,178 of 8,353 thumbnails". It never moves on from that point.

Reboot the computer and it starts again "Syncing 1 of 8,353 thumbnails", but never goes passed 1, it just sits there doing nothing.

I've tried uninstalling, rebooting, re-installing. No joy getting this to sync.

Any help would be appreciated.

SubNote: the previous version of iCloud for Windows App (14.x) sync worked.